Autovacuum cost limits throttle vacuum during peak I/O periods

Default autovacuum_vacuum_cost_delay (2ms) and autovacuum_vacuum_cost_limit (inherited from vacuum_cost_limit, typically -1 meaning use default) throttle autovacuum I/O to prevent impact on foreground queries. The cost limit is distributed among running autovacuum workers, potentially slowing vacuum operations when multiple workers are active.

Monitor postgresql.vacuum.count and vacuum completion times. If vacuums consistently fail to complete during low-activity windows, adjust autovacuum_vacuum_cost_limit upward. For systems with dedicated I/O capacity, increase cost limit or reduce cost delay. Track blk_read_time and blk_write_time to correlate vacuum throttling with I/O performance. Consider per-table cost settings for critical tables.